Pressure sensitive adhesive formulation including enhanced polyisobutylene modifier

ABSTRACT

An improved pressure sensitive adhesive includes a base polymer and a PIB modifier that is made up of a homopolymer of isobutylene wherein a predominant portion of the double bonds are in either an alpha position or a beta position. The modifier may function as a plasticizer, a tackifier extender or a combination plasticizer and tackifier extender for the pressure sensitive adhesive.

CROSS REFERENCE TO RELATED APPLICATION

None

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to pressure sensitive adhesives (PSAs)andthe like, and in particular to plasticizers and tackifier extenders forpressure sensitive adhesives. More particularly the invention relates toimproved pressure sensitive adhesives that incorporate enhancedpolyisobutylene (PIB) modifiers therein. The invention also relates tomethods for improving the tack strenghth and shear holding strength ofpressure sensitive adhesives by incorporating therein an enhanced PIBmodifier.

2. The Prior Art Background

Pressure sensitive adhesives are well known products having many uses,including, for example, and without limitation, use as an adhesive layerfor labels, packing tape, structural tape, medical tape and floor tiles.The adhesive properties of pressure sensitive adhesives and the lengthof time that the tackiness of such adhesives is retained may be improvedand enhanced by the incorporation in the adhesives of modifiers such asplasticizers and tackifier extenders. Plasticizers and tackifierextenders are often incorporated into the adhesive by adding the same tothe adhesive formulation during the production of the adhesive.Generally speaking, tackifier extenders are substances, which may beused in conjunction with conventional tackifying resins to achieve thesame degree of tack at a lower concentration of the tackifying resin.Plasticizers are substances that improve the physical characteristics ofan adhesive by making it softer and more ductile.

Conventional pressure sensitive adhesives typically include a basepolymer composition which may be a single polymer or a mixture ofpolymers, one or more plasticizers, one or more tackifying resins, andperhaps other additives such as fillers, antioxidants and solvents. Forexample, a high molecular weight (1,000,000 to 2,000,000 viscosityaverage molecular weight (VAMW), for example) polyisobutylene may alsobe used as a base polymer. Polyterpenes, which are usually solid, may beused as tackifying resins. Mineral oils may be used as plasticizers.Conventional polybutenes may be used as combination plasticizers andtackifier extenders. Additives may include fillers such as talc orcalcium carbonate, antioxidants, and solvents.

As mentioned above, the performance of pressure sensitive adhesives mayoften be improved and enhanced by the incorporation therein ofplasticizers and/or tackifier extenders. Conventional polybutene mayoften be used as both a plasticizer and a tackifier extender. Suchpolybutenes are simply added to the pressure sensitive adhesive (PSA)during formulation. The double bonds of these previously knownconventional polybutene materials are mostly internal. That is to say,it is normal for at least about 90% of the double bonds to be at aninternal position and for less than about 10% of the double bonds to bein a terminal (vinylidene) position. In addition, while the initialmonomeric mixtures used to produce these conventional polybutenes mayoften be predominantly isobutylene, the same may also incorporatessubstantial quantities of monomers other than isobutylene. Thus, theconventional polybutenes that have been used as tackifiers in the pastmay generally be referred to as copolymers or terpolymers. For example,such conventional polybutenes often and commonly incorporateapproximately 10% or so by weight of 1-butene and/or 2-butene, with onlyabout 90% of the monomeric units in the polymer being isobutylene units.

The incorporation of conventional polybutenes into the pressuresensitive adhesive is accomplished simply by introducing the polybuteneinto a vessel along with all of the other components of the pressuresensitive adhesive formulation and heating and blending the mixture.

SUMMARY OF THE INVENTION

In accordance with one aspect of the concepts and principles of thepresent invention a new and highly useful pressure sensitive adhesivewhich comprises a base polymer and a modifier. The modifier maydesirably be provided in the form of an enhanced PIB polymer productcomprising a homopolymer of isobutylene wherein a predominant portion ofthe double bonds are in an alpha or beta position. The modifier mayfunction as a plasticizer, a tackifier extender, or both. In furtheraccordance with the preferred aspects of the invention, the enhanced PIBpolymer product may desirably have a polydispersity no greater thanabout 2.2 and a number average molecular weight (MN) that is within therange of from about 900 to about 3000.

Preferably, in further accordance with the concepts and principles ofthe invention, at least about 95%, preferably at least about 96%,desirably at least about 97%, even more desirably at least about 98%,and ideally at least about 99% of the monomeric units incorporated inthe PIB modifier molecules are isobutylene moieties. Even moredesirably, no more than about 1% of the monomeric units incorporated inthe PIB modifier molecules are something other than isobutylenemoieties.

In still further accord with the concepts and principles of theinvention, at least about 40%, preferably at least about 50%, even morepreferably at least about 60%, desirably at least about 70%, moredesirably at least about 80%, even more desirably at least about 90%,and ideally more than 90% of the double bonds of the enhances PIBpolymeric modifier of the invention may be in the alpha position. In amost preferred form of the invention, no more than about 1% of thedouble bonds of the PIB polymer product are in a position other thanalpha or beta.

Desirably, after removal of any solvent used in the formulation of theimproved pressure sensitive adhesives of the invention, the same mayinclude from at least about 10 to about 60% or more by weight of theenhanced PIB plasticizer and tackifier extender.

The invention also provides a method for improving characteristics suchas the tack strength and shear strength properties of a pressuresensitive adhesive that comprises including an enhanced PIB plasticizerand tackifier extender in the pressure sensitive adhesive formulation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the concepts and principles of the present invention,and as set forth above, it has been discovered that many properties,including tack strength, shear strength, and viscoelasticity of apressure sensitive adhesive, can be improved, by incorporation therein,as a modifier, an enhanced PIB polymer product having a highervinylidene (terminal double bond) content than conventional polybutenesand which is comprised essentially of a homopolymer of isobutylenewherein no more than about 5% of the monomeric units of the homopolymercomprise something other than isobutylene monomers. Enhanced PIBmaterials suitable for use in connection with the present invention aredescribed in several co-pending patent applications which are owned bythe owner of the present application.

Patent application Ser. No. 09/515,790 filed on Feb. 29, 2000 andentitled “Process for Producing High Vinylidene Polyisobutylene” (the“'790 application”) describes a new process for the production, interalia, of enhanced polyisobutylene (PIB) products. Some grades ofenhanced PIB are referred to as high vinylidene PIB (HV-PIB) which alsomay sometimes be referred to as highly reactive PIB (HR-PIB). The termsHV-PIB and HR-PIB are essentially synonymous. The enhanced PIB may alsosometimes be characterized by the term isobutylene homopolymer.

Patent application Ser. No. 09/665,084 filed on Sep. 20, 2000 andentitled “Process for Preparing Polyolefin Products” (the “'084application”) describes the use of the process of the '790 applicationfor the production of polyolefins generally, including certain enhancedPIB polymer compositions. Patent application Ser. No. 10/102,279 filedMar. 19, 2002 and entitled “Mid-Range Vinylidene Content PolyisobutylenePolymer Product and Process for Producing the same” (the “'279application”) describes certain mid-range vinylidene containing enhancedPIB polymer compositions. The entireties of the disclosures of the '790,'084 and '279 applications are hereby incorporated into and made a partof the present disclosure by this specific reference thereto.

The number average molecular weight (M_(N)) of the enhanced PIB polymercompositions to be used as pressure sensitive adhesive modifiers inaccordance with the concepts and principles of the invention maydesirably range from about 900 to about 3000. The alpha position doublebond (vinylidene) content of the enhanced PIB products may desirablyrange from less than about 50% to more than about 90%, with theremainder of the double bonds ideally being in the beta position.Preferably, the polydispersity of the enhanced PIB product of theinvention may range from about 1.2 to about 2.2, depending upon themolecular weight of the polyisobutylene. Desirably, the amount ofisobutylene monomeric units incorporated in the enhanced PIB product tobe used as a pressure sensitive adhesive modifier should be at leastabout 95% and ideally may be about 99% or higher of the total monomericmoieties of the enhanced PIB product.

In accordance with the invention, the enhanced PIB to be used as amodifier to provide the improved pressure sensitive adhesive of theinvention may desirably and preferably be produced using the proceduresdescribed in the '790, the '084 and the '305 applications. Thus, a majorand extremely important feature of the invention is simply that theenhanced PIB to be used as a pressure sensitive adhesive modifier toprovide the improved properties, including improved tack and/or shearstrength, should desirably have a greater concentration of vinylidenedouble bonds, have a lower polydispersity, and have a higher percentageof isobutylene monomeric units than does conventional polybutene.Furthermore, the improved pressure sensitive adhesive product of theinvention may desirably include from at least about 10 to about 60% ormore by weight, after evaporation of any solvent used duringformulation, of the enhanced PIB modifier.

COMPARATIVE EXAMPLE

To establish the effectiveness of the enhanced PIB modifiers of theinvention, a pressure sensitive adhesive was prepared using an ExxonChemical high molecular weight polyisobutylene elastomer (Vistanex MML-120) as a base polymer, a Hercules polyterpene tackifier (PiccolyteS-115), toluene as a solvent, and an enhanced PIB modifier. A BPAmococonventional polybutene (H-300) was used as a modifier in a comparativesample employed to compare the properties of a pressure sensitiveadhesive formulated in accordance with the concepts and principles ofthe invention with the properties of a prior art pressure sensitiveadhesive.

In accordance with the invention, an enhanced PIB modifier was producedemploying the loop reactor described in the '790 application identifiedabove. The catalyst composition consisted of a premixed BF₃/methanolcomplex wherein the ratio of BF₃ to methanol was about 1:1. The reactionmixture was maintained at a temperature of from about 50 to about 60°F., and the residence time was controlled at about 120 seconds. Theresultant enhanced PIB product (TPC 1160) had a number average molecularweight (M_(N)) of approximately 1600, an average alpha position doublebond (vinylidene) content of about 60% and an average beta positiondouble bond content of about 40%. That is to say, essentially all of thePIB molecules of the TPC 1160 product contained either alpha positiondouble bonds or beta position double bonds and essentially nonecontained the isomeric tetra substituted double bonds. In addition, atleast about 99% of the monomeric units of the enhanced TPC 1160 productwere isobutylene moieties, and the polydispersity of the enhanced TPC1160 product was about 1.4. The TPC 1160 PIB material is approximatelyhalf as viscous as conventional polybutenes such as BPAmoco H-300. Thisresults in easier handling during the formulation of pressure sensitiveadhesives.

Exxon Vistanex MM L-120 is a commercially available tough, rubber solidpolyisobutylene polymer having the following properties:

Specific gravity 0.92 Color white to pale yellow Ash, wt % 0.3 maxVolatiles, wt % 0.3 max Stabilizer, wt % 0.10% Staudinger Viscosity99,000-117,000 Molecular Weight Flory Viscosity Average1,450,000-1,870,000 Molecular Weight Intrinsic Viscosity (dl/g)3.16-3.72

Piccolyte S-115 is a commercially available pale, inert, low molecularweight, thermoplastic hydrocarbon resin that is produced from monomericbeta-terpene. It has the following typical properties:

Softening point, R & B, ° C. 115 Color, Gardner 2 Bromine number 30Density at 25° C., kg/l 0.99 Ash, % 0.1 Flashpoint, COC, ° C. 234 Meltviscosity, ° C., 1 poise 220 10 poises 175 100 poises 150

The TPC 1160 modifier product described above was incorporated into apressure sensitive adhesive using standard pressure sensitive adhesiveproduction methodology. The TPC 1160 PIB modifier concentration in thefinished pressure sensitive adhesive, after evaporation of the solvent,was approximately 30.6%. The formulation before removal of the toluenesolvent was as follows:

Vistanex MM L120 100 parts by weight Piccolyte S-115 70 parts by weightTPC 1160 75 parts by weight Toluene 980 parts by weight

For comparative purposes, a similar pressure sensitive adhesive wasproduced using essentially the same methodology except that in this casea commercially available conventional polybutene (BPAmoco H-300) wasused as the modifier instead of the TPC 1160. BPAmoco H-300 is aconventional polybutene with low vinylidene content (typically<10%). TheM_(N) of the BPAmoco H-300 was about 1600 and its polydispersity was inthe range of 1.8 to 2.0.

Tack strengths of the two pressure sensitive adhesives were measured inaccordance with ASTM D2979 probe tack test. The resulting tack strengthdata as shown in Table 1 illustrates the fact that the tack strength ofthe TPC 1160 modified pressure sensitive adhesive formulation is 2 to 3times higher than the tack strength of the conventional polybuteneformulation.

TABLE 1 Tack strength (N*μm) Rate of Displacement TPC 1160 H-300(μm/sec) PSA Formulation PSA Formulation 1.0 45 16 5.0 47 23 10 65 31

Shear strengths were measure in accordance with ASTM D3654. Theresulting shear strength data as depicted in Table 2 shows that theshear strength of the PIB 1160 modified pressure sensitive adhesiveformulation is about 10% better than the tack strength of theconventional polybutene modified formulation.

TABLE 2 Shear Strength Time to Failure (hrs) at 18° C. TPC 1160 15.4modified PSA H-300 modified 13.8 PSA

The linear viscoelastic region of the TPC 1160 modified pressuresensitive adhesive formulation as depicted in Table 3 is four times thatof the conventional polybutene modified formulation.

TABLE 3 Rheological Test Results Linear Viscoelastic Range (N*μm) TPC1160 modified PSA 0-2000 H-300 modified PSA 0-500 

Summarizing the foregoing, when pressure sensitive adhesives areimproved in accordance with the concepts and principles of the inventionby incorporating therein the enhanced PIB product modifier of theinvention, the improved pressure sensitive adhesives have improvedend-use application due to the fact that the enhanced PIB modifierproduct:

(1) provides higher tack and shear strength due at least in part to thehigh purity and consistency of the enhanced PIB;

(2) provides improved handling because it has a lower viscosity atambient conditions than conventional polybutenes;

(3) provides improved plasticizing ability over conventionalpolybutenes; and

(4) provides improved viscoelasticity when compared with conventionalpolybutenes.

In the preferred embodiments of the invention described above, anenhanced PIB modifier was used to improve the properties of a basepolymer/tackifier system comprising a high molecular weightpolyisobutylene elastomeric base polymer and a polyterpene resintackifier. However, the invention is not limited to this specific basepolymer/tackifier pressure sensitive adhesive system. That is to say,the enhanced PIB modifier product of the invention is suitable forincorporation in and providing improved properties to a number ofpressure sensitive adhesive systems, wherein the base polymer comprises,for example, a styrene butadiene rubber, a natural rubber, apolyacrylate, an ethylene/butylene/isoprene block copolymer, or anethylene vinyl acetate copolymer, and the tackifying resin comprises,for example, a rosin, a terpene resin, or a pinene. Specifically, butwithout limitation, the enhanced PIB modifier product of the inventionmay be used to improve the properties of systems comprising, forexample, (1) a natural rubber base polymer and a resin emulsiontackifier (Hevereaz C-200; Heavetex Corp.); (2) a styrene butadienerubber base polymer and a low molecular weight flowable butyl rubbertackifier derived from virgin butyl rubber (Kalene 800, 800V70, 1300 or1300V70; Elementis Specialty Performance Polymers); (3) astyrene/isoprene/styrene block copolymer base polymer and a C₅hydrocarbon resin tackifier (Wingtack 86 or 95; Goodyear); (4) a styrenebutadiene rubber base polymer and a terpene phenolic resin tackifier(Nirez 300, 2019, 7042, V-2040, V-2040HM or V-2150; Arizona ChemicalCo.); and (5) a natural rubber base polymer and a terpene phenolic resintackifier (Nirez 300, 2019, 7042, V-2040, V-2040HM or V-2150).Specifically, the enhanced PIB modifier product of the invention may beused as a tackifier extender and/or as a plasticizer in each of the basepolymer/tackifier systems identified above, as well as in each and everybase polymer/tackifier system where conventional polybutenes have beenused previously as a tackifier, as a plasticizer, as both a tackifierextender and a plasticizer or simply as a modifier for any otherpurpose.

I claim:
 1. An improved pressure sensitive adhesive comprising a basepolymer and a PIB modifier, said PIB modifier comprising a homopolymerof isobutylene wherein a predominant portion of the double bonds are ineither an alpha position or a beta position.
 2. An improved pressuresensitive adhesive as set forth in claim 1, wherein said base polymerfurther comprises a polyolefin elastomer.
 3. An improved pressuresensitive adhesive as set forth in claim 1, wherein said PIB modifierhas a polydispersity no greater than about 2.2.
 4. An improved pressuresensitive adhesive as set forth in claim 1, wherein said PIB modifierhas a M_(N) no greater than about
 3000. 5. An improved pressuresensitive adhesive as set forth in claim 4, wherein said PIB modifierhas a M_(N) which is at least about
 900. 6. An improved pressuresensitive adhesive as set forth in claim 1, wherein at least about 95%of the monomeric units incorporated in the PIB modifier molecules areisobutylene moieties.
 7. An improved pressure sensitive adhesive as setforth in claim 1, wherein at least about 97% of the monomeric unitsincorporated in the PIB modifier molecules are isobutylene moieties. 8.An improved pressure sensitive adhesive as set forth in claim 1, whereinat least about 99% of the monomeric units incorporated in the PIBmodifier molecules are isobutylene moieties.
 9. An improved pressuresensitive adhesive as set forth in claim 1, wherein no more than about1% of the monomeric units incorporated in the PIB modifier molecules aresomething other than isobutylene moieties.
 10. An improved pressuresensitive adhesive as set forth in claim 1, wherein at least about 40%of the double bonds of the PIB modifier molecules are in the alphaposition.
 11. An improved pressure sensitive adhesive as set forth inclaim 1, wherein at least about 50% of the double bonds of the PIBmodifier molecules are in the alpha position.
 12. An improved pressuresensitive adhesive as set forth in claim 1, wherein at least about 60%of the double bonds of the PIB modifier are in the alpha position. 13.An improved pressure sensitive adhesive as set forth in claim 1, whereinat least about 70% of the double bonds of the PIB modifier molecules arein the alpha position.
 14. An improved pressure sensitive adhesive asset forth in claim 1, wherein at least about 80% of the double bonds ofthe PIB modifier molecules are in the alpha position.
 15. An improvedpressure sensitive adhesive as set forth in claim 1, wherein at leastabout 90% of the double bonds of the PIB modifier molecules are in thealpha position.
 16. An improved pressure sensitive adhesive as set forthin claim 1, wherein more than 90% of the double bonds of the PIPmodifier molecules are in the alpha position.
 17. An improved pressuresensitive adhesive as set forth in claim 1, 10, 11, 12, 13, 14, 15, or16, wherein no more than about 1% of the double bonds of the PIBmodifier molecules are in a position other than alpha or beta.
 18. Animproved pressure sensitive adhesive as set forth in claim 1, 2, 3, 6,7, 9, 10, 11, 12, 13, 14, 15, or 16, wherein said pressure sensitiveadhesive comprises from about 10 to about 60% by weight of said PIBmodifier.
 19. An improved pressure sensitive adhesive as set forth inclaim 1, 2, 3, 6, 7, 9, 10, 11, 12, 13, 14, 15, or 16, wherein said PIBmodifier is a tackifier extender.
 20. An improved pressure sensitiveadhesive as set forth in claim 1, 2, 3, 6, 7, 9, 10, 11, 12, 13, 14, 15,or 16, wherein said PIB modifier is a plasticizer.
 21. An improvedpressure sensitive adhesive as set forth in claim 1, 2, 3, 6, 7, 9, 10,11, 12, 13, 14, 15, or 16, wherein said PIB modifier is a plasticizerand a tackifier extender.